AbstractThe Calabrian Arc is a narrow subduction-rollback system resulting from Africa/Eurasia plate convergence. We analysed the structural style of the frontal accretionary wedge through a multi-scale geophysical approach. Pre-stack depth-migrated crustal-scale seismic profiles unravelled the overall geometry of the subduction complex; high-resolution multi-channel seismic and sub-bottom CHIRP profiles, together with morpho-structural maps, integrated deep data and constrained the fine structure of the frontal accretionary wedge, as well as deformation processes along the outer deformation front.

We identified four main morpho-structural domains in the western lobe of the frontal wedge: the proto-deformation area at the transition with the abyssal plain; two regions of gentle and tight folding; a hummocky morphology domain with deep depressions and intervening structural highs; a highstanding plateau at the landward limit of the salt-bearing accretionary wedge, where the detachment cuts through deeper levels down to the basement. Variation of structural style and seafloor morphology in these domains are related to a progressively more intense deformation towards the inner wedge, while abrupt changes are linked to inherited structures in the lower African plate. Our data suggest focusing of intense shallow deformation in correspondence of deeply rooted faults and basement highs of the incoming plate.

Back-arc extension in the Southern Tyrrhenian Sea has recently ceased, producing a slowdown of slab rollback and plate-boundary re-organization along trans-tensional lithospheric faults segmenting the continental margin. In this complex setting, it is not clear if the accretionary wedge is still growing through frontal accretion. Our data suggest that shortening is still active at the toe of the wedge, and uplift rates along single folds are in the range of 0.25-1.5 mm/yr. An unconformity within the Plio-Quaternary sediments suggests a discontinuity in sedimentation and tectonic processes, i.e. a slowdown of shortening rate or an increase in sedimentation rate, but not a real inactivation of frontal accretion, which still contributes to the migration of the outer deformation front towards the foreland.

AbstractAmong the many cases studied of mass-transport deposits in continental margins, the role of basin topography in controlling the types, distribution, architecture and emplacement of such deposits has not been properly remarked.
In the western portion of Northern Apennine foothills, masstransport deposits form two composite Messinian mass-wasting bodies that reveal progressive development strictly controlled by basin topography. Extensively analyzed through stratigraphic and structural studies, they form two major elliptical-shaped bodies in map view; maximum 10 kilometres wide, tens of kilometres in length and with estimated volumes of about 250 km3 each, they are elongated parallel to NW-SE oriented thrust fronts. They are coalescing chaotic masses that consist, at the base, of debris flows formed by monogenic gypsum arenite or breccia and decametric blocks of primary gypsum, whereas at the top they are made up of kilometres-wide outliers of pre-gyspum deposits, which slid away from partially preserved headwall scarps. In the external accumulation zone, the mass wasted deposits show imbricate thrust-stacks composed of scraped-off gypsum debris flow deposits. The types, distribution, architecture and emplacement of the studied mass-transport deposits testify the strict control of the wedge-top basins morphology. The internal and steeper flank of the wedge-top basins was representing the depletion zone of sliding masses; whereas, the outer and less steep flank of the wedge-top basins stopped the moving masses and formed the accumulation zones. The relief of the wedge-top basins was progressively modifying during the intra-Messinian tectonic pulse that, affecting the entire Northern Apennine orogenic wedge, triggered the studied mass-transport deposits.

AbstractA petrological investigation has been carried out on the Late Miocene (around 5.5 Ma) volcaniclastic layer interbedded in the uppermost Messinian deep-water sediments of the Northern Apennines foredeep basin. The studied samples derive from five sections located on a 200 km long area and reveal that the volcaniclastic layer corresponds to centimetric- to metric-thick turbiditic sequence, essentially composed of lapilli to ash-sized glass shards and scarce (<5%) mineral fragments. The homogeneous chemical composition, of the glass shards (calc-alkaline rhyolite) and crystals (plagioclase, sanidine, biotite) suggests a cogenetic origin for the studied samples.
In these samples non-volcanic detritus is absent and the morphology of the glass shards is indicative of an origin by an explosive magmatic eruption. Morphological, geochemical and sedimentological features suggest that the volcaniclastic layer can be considered as «primary monomagmatic turbidite» resulting directly from the eruptive vent of a calc-alkaline rhyolitic volcanic arc system. None of the coeval outcropping volcanoes, up to a distance of 1500 km from the studied sections, can be considered as the possible source of this layer. Nevertheless, tectono-magmatic evidence suggests that it may represent the witness of the activity of a calc-alkaline submarine volcanic arc located northwestward of the Aeolian Arc, and related to the first rifting-spreading episode of the Southern Tyrrhenian region.